An arc flash event generally occurs when air is ionized to conduct electrical energy between two conductors that have a voltage potential. During an arc flash event, energy is released that may cause burns and other injuries to anyone or anything that is in proximity to the event. Under requirements from the Occupational Safety and Health Administration (OSHA), employers are required to categorize arc flash hazard potential in areas where workers are required to conduct work on or near live electrical equipment, and to provide proper guidelines on proper protective wear and safe working distances for their workers. In order to categorize the arc flash hazard potential, a detailed study of the electrical system is generally required to determine: the short circuit current availability, the distance from the power supply station, the infrastructure connecting the particular node to the power supply station, and details about the circuit breaker safety shut-offs and their response-time profiles.
Generally, the most costly parameter to estimate is the short circuit current available (SCCA), which is a measure of the amount of current that can be drawn from a particular node in an alternating current (AC) electrical circuit in the event of a short-circuit event. Once an accurate estimate of SCCA is made, determining the arc flash hazard potential can be performed according to the methods provided in, for example, publication 1584 of the Institute of Electrical and Electronics Engineers (IEEE 1584). Similarly, the arc flash hazard potential category can be determined according to the methods provided in standard 70E of the National Fire Protection Association (NFPA 70E). The arc flash hazard potential and arc flash hazard potential category can be used by workers to, for example, identify a safe working distance, select suitable personal protective wear, and to otherwise maintain a safe working environment. Typically, estimations of SCCA are made by considering the distance of the particular node from the power generation station, the nature of the transformers connecting the particular node to the power distribution system supply wires, and the gauge and materials of the conductors connecting the particular node to the transformers. But these methods may undesirably lead to over-estimates of SCCA.
Overestimates of SCCA can be dangerous and may lead to lower calculated incident energy in the event of an arc flash than the risk that is actually presented, because many protective devices have inverse, or extremely inverse time-response curves such that a very high-current arc flash will trigger the protective device very quickly and result in less incident energy than a relatively low-current arc flash that is allowed to endure for a longer duration due to the delayed reaction of the protective device. It is desirable, therefore, to accurately estimate SCCA at a particular node in an AC electrical circuit. Furthermore, it is desirable to estimate SCCA dynamically, and in real time so as to provide updated SCCA information as SCCA changes due to, for example, changes in the configuration of the power distribution system.